The present invention relates generally to vapor or gaseous discharge lamps, and more particularly to germicidal lamps.
All vapor lamps have a limited life. One type of vapor lamp, a low pressure mercury lamp, uses an electrode having emission material thereon. A quartz envelope is used to contain the low pressure mercury within the lamp. Often, the emission material on the electrode is a factor in the life of the lamp and its failure. The emission material is slowly consumed during the operation of the lamp. When the emission material on the electrode is totally consumed, the lamp will reach the end of its life. When the emission material is consumed, there is a sudden increase in cathode fall voltage resulting in a sharp raise in lamp voltage, typically over 100 volts. For lamps having a rapid start or preheat ballast, this voltage increase rises the lamp voltage to a level that approximates the open circuit voltage, and the lamp will shut down. However, in applications where an instant start operation is used, this open circuit voltage is typically three or four times the lamp""s operating voltage and the lamp will continue to operate despite the voltage increase. The continued operation of the lamp is not desirable, since the voltage increase will cause a great increase in wattage consumed at the lamp""s end. Also, the resulting arc consumes the electrode and support structure. The temperatures at the base will rise to a level sufficient to melt the socket and burn the housing components. The lamp and related structures can be severely damaged if the lamp does not shut down.
There have been several solutions proposed in efforts to solve the uncontrolled operation of a vapor lamp at the end of its life to prevent this destructive and dangerous condition. In the past, thermal fuses have been used in the lamp base. Additionally, electronic shut down circuits that sense increased voltage or rectification have been used. While many of these solutions have been useful, they are often expensive and sometimes do not work properly. One solution that is promising is to utilize an arc quenching device within the lamp itself. As the lamp arcs back to the support structure, the temperature rise may be used to activate a material that raises the voltage by hundreds of volts to effectively shut down the lamp. A hydrogen containing gas may be liberated to cause a great voltage increase and cause the lamp to shut down.
An example of an arc quenching material is disclosed in U.S. Pat. No. 5,705,887 entitled xe2x80x9cFluorescent Lamp With End of Life Arc Quenching Structurexe2x80x9d issuing to Schaffer on Jan. 6, 1998. Therein disclosed is a metal hydride material applied to the top of a lamp stem. Upon an increase in temperature at the end of life of the lamp, hydrogen gas is released by the disassociation of the hydride and the lamp is caused to shut down. However, for this solution to be effective, it is important that the hydride not decompose in normal lamp operation and that the temperatures experienced in lamp manufacture not decompose the hydride. Therefore, for many lamps, there is no metal hydride available which can be used.
For example, germicidal lamps or other vapor lamps using a quartz envelope that require sealing temperatures of approximately 1600xc2x0 C. have special problems. There is no metal hydride which is stable at the sealing temperatures required for the manufacture of lamps having quartz envelopes. Additionally, there is essentially no room or site on the mount structure to apply a coating.
In germicidal lamps, it is particularly important to have a reliable shut down mechanism at the end of life of the lamp. Many germicidal lamps are operated in pressurized sealed vessels for water treatment. The lamp end and sleeves are sealed to the vessels with o-rings or gaskets clamped with compression fittings. If this seal integrity is compromised due to damage as the result of arcing of the vapor lamp at the end of its life, the damage may result in the lamp and sleeve being violently expelled from the vessel, causing injuries, flooding and total system failure. Therefore, there is a need for a safe, reliable and easy to implement arc quenching device for use with germicidal lamps or other lamps utilizing a quartz envelope and requiring high temperatures during manufacture.
The present invention comprises a vapor lamp or gaseous discharge lamp having a quartz envelope containing a filament and lead wire. The lead wire is held in a stem and coupled to an exterior contact pin. Mica or hydrous aluminum silicate mineral is placed on the lead wire between the filament and the stem. The mica releases hydrogen when subjected to high temperatures, effectively quenching the arc formed at the end of the lamps life.
Accordingly, it is an object of the present invention to prevent damage to a vapor lamp and fixture when the vapor lamp reaches its end of life.
It is a further object of the present invention to provide a simple, inexpensive solution to end of life arcing within a vapor lamp.
It is an advantage of the present invention that it may be used with high sealing temperatures that occur in the manufacture of vapor lamps having quartz envelopes.
It is an advantage of the present invention that it does not affect the normal operation of the vapor lamp.
It is another advantage of the present invention that it can withstand high sealing temperatures required during manufacture of lamps with quartz envelopes.
It is a feature of the present invention that mica is attached to a lead wire below the filament.
It is another feature of the present invention that the mica is held on a lead wire with a ferrule.
These and other objects, advantages, and features will become readily apparent in view of the following more detailed description.